The instant invention relates to a cutting and reshaping press with a hydro-mechanical articulated lever drive in which the drive cylinder of a ram is supported by a bridge structure located in the stanchion between lateral guides. The ram is connected to the stanchion by means of threaded spindles or other means capable of being adjusted in height, the bridge construction thereby being adjustable within the free space formed within the frame-shaped stanchion.
German Pat. No. 29 25 416 discloses an articulated lever press to cut sheet metal. The structure disclosed therein comprises a "differential-path" press having a pressure cylinder drive located between two articulated-lever systems. The drive's piston engages by the end of its piston rod a connection articulation comprising two control arms in the middle of the press. The piston is linked by its other end to the articulated lever systems (the articulations of said articulated-lever systems bending outward to point to the middle of the press and being symmetrical in relation to said middle), whereby the connection articulation, assisted by the press ram, is provided with a guidance transversely to the direction of the piston rod. The press is characterized in that the support for the pressure cylinder drive is on the press ram. The ram may be fashioned in the form of a frame.
U.S. Pat. No. 2,087,811 and British Pat. No. 804,352 were indicated therein as the authoritative state of the art. According to these published patents the stroke path of the ram is defined by the stroke of the fixed drive cylinder attached to the frame and by the multiplication ratio which results in a known manner from the articulated-lever drive and from the type of control arm used.
The development of the differential-path press begun by the applicant some 10 years ago has proven itself very well as the publications listed at the end of the description testify.
The observations made and especially the intensive investigation of over 100 completed differential-path presses which have given top performance in the most varied types of reshaping techniques lead however to the conclusion that, while essential advantages over the classic press systems are proven beyond doubt, several significant changes in the system seem advisable in the interest of even greater improvements.
The following individual facts were taken into consideration:
a. Ram Speed
Investigations have shown that the differential-path press has a high idling speed and a very slow forming speed.
The resulting advantages have been described in the cited publications, but internal investigations and experience gained in the field led to the conclusion that the retardation attained in the differential-path press which is 8 or 10 times that of an eccentric press, yields truly good results but that conversely no retardation beyond this length is necessary.
Forming over the 5 times greater area of an "eccentric press" finally has the same effect and offers a shorter rhythmic sequence.
In addition it was also shown that the high idling speed, especially during the back stroke, does not tolerate any additional increase in the number of strokes because of the very long braking path of the ram in the upper dead center, i.e. the stroke capacity of the differential-path press is approximately 10 to 20% below that of an eccentric press. Added to this is yet another handicap in case of an automated press as insufficient time is available for the automation equipment so that the press is slowed down overall as a result because it must always wait for the completion of the operations of these items of equipment which are as a rule operated in a sequence that is under constrained control. On the other hand the significant advantages of the differential-path press appear clearly, even with only five times the reshaping range of the eccentric press.
A comparison between velocity sequences of the eccentric press, of the differential-path press and of the press according to the instant invention confirms this clearly (see FIG. 4).
(b) Progression of forces as a function of distance from the lower dead center
It was found that the differential-path press has a much greater work capacity at a rating equal to that of a comparable eccentric press because it does not work on drive force.
The progression of its pressure force in the lower dead center lies, depending upon the manufacturer, usually above that of an eccentric press, however the curve decreases more rapidly than for an eccentric press as the distance from the lower dead center increases.
For this reason, the progression of the curve of the pressure as a function of the distance from the lower dead center should be raised in the intended new development, and in order to achieve this it is no longer possible to avoid modifying the system.
In this context it must be noted that the differential-path press was developed on the basis of considerations that the hydraulic cylinder participates in the stroke of the ram, resulting in approximately 25% energy savings.
It was found however that the great advantage of this press can also lead to considerable tilting movements of the hydraulic cylinder when an eccentric load is applied because of the distance between the lower edge of the ram, the suspension point and the cylinder fastening, and such movements may often provoke a rupture of the piston rod or of the piston rod fastening as the central piece is then guided separately in the frame so that tensions cannot always be absorbed in this area when eccentric loads apply.
When the differential-path press is used as a stamping press it is also possible to attain die tool lives 30 times longer than is the case with a spindle press although large-size bearings are required. It is however not possible to enlarge these bearings, if only because of space availability considerations in differential-path presses.
Based on these considerations it is the objective of the instant invention to define a press of the type described initially herein with velocity characteristics that make it possible to achieve a slower idling speed, better and more precise braking capability and thereby better controllability and an increased number of strokes, whereby the pressure multiplication ratio is selected in relation to that of the differential-path press so that the stroke of the drive cylinder is considerably greater than the stroke of the ram.